Occurs especially in individuals with
incompetent lips, i.e. lips that do not meet at rest.
Underlying aetiology is commonly a discrepancy between the maxillary dentition and the mandibular dentition, known as a Class II malocclusion, classified by Angle. As it is the basal bone that supports these teeth, the discrepancy is usually skeletal, ie teeth on a Skeletal II base. Some are known classically as adenoid facies, ie long pale face, narrow palate, large adenoids blocking the airways.
Problems associated with being a mouth breather include a dry mouth, hyperplastic gingivitis (the gums grow larger and redder as they are perpetually dried up) and the fact that people think you look less
intelligent.